DIESEL DYNAMIC TIMING TIMING SPECIFICATION

MODELS AFFECTED: ALL MODELS EQUIPPED WITH A 4.3L OR 5.7L DIESEL

Timing specifications for the 5.7L and 4.3L diesel engines are based upon use of a luminosity timing method available from many suppliers, such as Snap-On, Kent-Moore, Owatonna and Sun. Any other type of device that measures something other than luminosity (such as pressure impulse) will not correlate with the specifications and should not be used.

The Kent-Moore dynamic timing meter has two pick-ups. One pick-up measures the pressure impulse in the injection pipe and the other pick-up measures luminosity through a probe in the glow plug hole. When using this equipment, be sure to use the luminosity pick-up rather than the impulse pick-up.

Timing specifications are located on the "vehicle emissions control information" label for 1983 and 1984 vehicles. Past model (1978-1982) specifications are reprinted below from Serviceman Bulletin 1-82-87 for your reference. Low Altitude High Altitude Counties Counties -------- -------- Year Engine Timing RPM Timing RPM ---- ------- ------ --- ------- --- 1978 5.7L -4 1/2 DEG 1200 -5 1/2 DEG 1200 1979 5.7L -4 1/2 DEG 1200 -5 1/2 DEG 1200 1980 5.7L -4 1/2 DEG 1200 -5 1/2 DEG 1200 1981 5.7L -4 DEG 1200 -5 DEG 1200

1982 5.7L Low Altitude -4 DEG 1250 -5 DEG 1250 Emissions Package 5.7L High Altitude -3 DEG 1250 -4 DEG 1250 Emissions Package

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.